The present invention relates to a propylene-based copolymer composition, and more particularly, to a propylene-based copolymer composition which is excellent not only in heat resistance, flexibility and transparency, but also in mechanical properties such as tensile strength and impact resistance.
Propylene homopolymer has been extensively used in various applications such as injection-molded products, sheets, films and containers because of excellent heat resistance and stiffness thereof. Further, it has been positively studied to use polyolefins as alternate materials for building materials such as decorative sheets, and packages for foodstuffs, which have been conventionally made of polyvinyl chloride. For this reason, it has been required to develop polyolefins capable of exhibiting excellent flexibility, heat resistance and transparency. The propylene homopolymer is excellent in heat resistance but is deteriorated in flexibility and transparency. Also, polyethylene and ethylene/xcex1-olefin copolymers are excellent in flexibility and transparency but are deteriorated in heat resistance. In consequence, these polyolefins are used only in limited applications.
In the above application fields, there have been conventionally used random copolymers produced by copolymerizing propylene with a small amount of ethylene and/or an xcex1-olefin having 4 to 6 carbon atoms. These random copolymers are excellent in transparency but exhibit only a low flexibility. Further, the copolymers suffer from such an essential problem that the heat resistance thereof is considerably deteriorated.
As the method of improving the flexibility and transparency of polypropylene, for example in Japanese Patent Application Laid-Open (KOKAI) No. 8-100037(1996), there has been proposed a process for the production of propylene/ethylene block copolymers exhibiting excellent heat resistance and flexibility comprising producing a propylene homopolymer having a specific intrinsic viscosity ratio and then producing a copolymer having an ethylene content of 25 to 65% by weight by a two-stage polymerization. Also, in Japanese Patent Application Laid-Open (KOKAI) Nos. 10-316810(1998) and 11-92619(1999), there have been described propylene-based block copolymers containing random polypropylene as matrix and exhibiting good flexibility and transparency.
However, propylene-based polymer compositions which are well-balanced and improved in heat resistance, transparency and flexibility, have not been obtained until now.
As a result of the present inventors"" earnest studies for solving the above problems, it has been found that by first producing a specific polymer component (A) comprising propylene as a main component, and then producing a specific copolymer component (B) comprising propylene and other xcex1-olefin having not more than 8 carbon atoms and containing propylene and ethylene as essential components, the obtained propylene-based copolymer composition can exhibit not only good flexibility and transparency, but also excellent mechanical properties such as tensile strength and impact resistance. The present invention has been attained based on this finding.
An object of the present invention is to provide a propylene-based copolymer composition exhibiting not only excellent flexibility and transparency as well as heat resistance substantially identical to that of propylene homopolymer, but also excellent mechanical properties such as tensile strength and impact resistance.
To accomplish the aim, in a first aspect of the present invention, there is provided a propylene-based copolymer composition comprising:
10 to 60% by weight of a polymer component (A); and
40 to 90% by weight of a copolymer component (B),
wherein said composition is obtained by producing the component (A) by first-stage polymerization and then producing the component (B) by second-stage polymerization,
wherein said polymer component (A) comprises propylene as a main component and has an isotactic index of not less than 90%, and
said copolymer component (B) comprises propylene and other xcex1-olefin having not more than 8 carbon atoms and contains propylene and ethylene as essential components,
said copolymer component containing a fraction insoluble in xylene at room temperature (hereinafter referred to as xe2x80x9ccold xylene insolublesxe2x80x9d) in an amount of from more than 20 to 70% by weight based on the weight of whole polymers, and a fraction soluble in xylene at room temperature (hereinafter referred to as xe2x80x9ccold xylene solublesxe2x80x9d) in an amount of 10 to 60% by weight based on the weight of whole polymers, and said cold xylene solubles containing an xcex1-olefin other than propylene in an amount of less than 20% by weight.
In a second aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspect of the present invention, wherein said component (A) is a propylene homopolymer, and other xcex1-olefin having not more than 8 carbon atoms of said component (B) is ethylene.
In a third aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspects of the present invention, which has a flexural modulus of 100 to 600 MPa, a haze of a 2 mm-thick sheet of not more than 70%; and a tensile strength at break of not less than 30 MPa.
In a fourth aspect of the present invention, there is provided the propylene-based copolymer composition according to the above aspects of the present invention, which satisfies the followings (1) to (4):
(1) a propylene content of 85 to 95% by weight;
(2) a content of the cold xylene solubles (hereinafter sometimes referred to merely as xe2x80x9cCXSxe2x80x9d) in the whole polymers of 10 to 60% by weight;
(3) a content (wt. %) of the xcex1-olefin other than propylene (hereinafter sometimes referred to merely as xe2x80x9cxcex1txe2x80x9d) and the content of the cold xylene solubles (CXS), satisfying the following formula:
CXS greater than 5xcex1txe2x88x9225 (5xe2x89xa6xcex1txe2x89xa615); 
and
(4) a melting peak temperature of not less than 160xc2x0 C.
The present invention will be described in detail below.
The component (A) as one of constituents of the propylene-based copolymer composition according to the present invention, is a polymer comprising propylene as a main component and has an isotactic index of not less than 90%. The component (A) is usually composed of crystalline cold xylene insolubles and amorphous cold xylene solubles. The content of the cold xylene insolubles is substantially identical to the isotactic index.
Here, the polymer comprising propylene as a main component means such a polymer containing propylene-derived constituent units in an amount of usually not less than 70% by weight, preferably not less than 90% by weight, more preferably not less than 95% by weight based on the weight of the polymer. The most preferred polymer comprising propylene as a main component is a propylene homopolymer.
When the isotactic index of the component (A) is less than 90%, the obtained composition tends to be deteriorated in heat resistance.
The component (B) as the other constituent of the propylene-based copolymer composition according to the present invention, is a copolymer of propylene and other xcex1-olefin having 2 to 8 carbon atoms, which comprises propylene and ethylene as essential components.
Examples of other xcex1-olefins used in the present invention may include, in addition to ethylene as the essential component, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene or the like. The more preferred copolymers are those produced only from propylene and ethylene.
In accordance with the present invention, the copolymer component (B) contains cold xylene insolubles in an amount of from more than 20 to 70% by weight based on the weight of whole polymers, and cold xylene solubles in an amount of 10 to 60% by weight based on the weight of whole polymers, and further the cold xylene solubles contains the xcex1-olefin other than propylene in an amount of less than 20% by weight. It is preferred that the content of the cold xylene insolubles is 25 to 60% by weight based on the weight of whole polymers; the content of the cold xylene solubles is 15 to 60% by weight on the weight of whole polymers; and the content of the xcex1-olefin other than propylene in the cold xylene solubles is 10 to 18% by weight.
Meanwhile, the xe2x80x9cwhole polymersxe2x80x9d used herein represent total polymers of the components (A) and (B).
When the component (B) contains the cold xylene insolubles in an amount of not more than 20% by weight, the obtained composition tends to be deteriorated in transparency. On the other hand, when the component (B) contains the cold xylene insolubles in an amount of more than 70% by weight, the obtained composition tends to be deteriorated in flexibility. In addition, when the component (B) contains the cold xylene solubles in an amount of less than 10% by weight, the obtained composition tends to be insufficient in flexibility. On the other hand, when the component (B) contains the cold xylene solubles in an amount of more than 60% by weight, the obtained composition tends to be deteriorated in heat resistance.
When the cold xylene solubles contains the xcex1-olefin other than propylene in an amount of not less than 20% by weight, the obtained composition tends to be deteriorated in transparency.
The propylene-based copolymer composition of the present invention comprises 10 to 60% by weight of the component (A) and 40 to 90% by weight of the component (B), preferably 20 to 50% by weight of the component (A), and preferably 50 to 80% by weight of the component (B).
When the content of the component (A) is less than 10% by weight and the content of the component (B) is more than 90% by weight, the obtained composition tends to be deteriorated in heat resistance. On the other hand, when the content of the component (A) is more than 60% by weight and the content of the component (B) is less than 40% by weight, it becomes difficult to obtain a composition having good flexibility and transparency.
It is preferred that the propylene-based copolymer composition of the present invention has as a whole the followings (1) to (4).
(1) a propylene content of 85 to 95% by weight;
(2) a content of the cold xylene solubles (CXS) in the whole polymers of 10 to 60% by weight;
(3) a content of the xcex1-olefin other than propylene (xcex1t; unit: wt. %) and the content of the cold xylene solubles (CXS), satisfying the following formula:
CXS greater than 5xcex1txe2x88x9225 (5xe2x89xa6xcex1txe2x89xa615); 
and
(4) a melting peak temperature of not less than 160xc2x0 C.
The propylene content and the content of the xcex1-olefin other than propylene having 2 to 8 carbon atoms (xcex1t) are in the range of 85 to 95% by weight and 5 to 15% by weight, respectively.
The propylene content is more preferably 87 to 95% by weight, still more preferably 88 to 92% by weight. The xcex1-olefin content (xcex1t) is more preferably 5 to 13% by weight, still more preferably 8 to 12% by weight. When the propylene content is more than 95% by weight and the xcex1-olefin content (xcex1t) is less than 5% by weight, the obtained composition may tend to be deteriorated in flexibility. On the other hand, when the propylene content is less than 85% by weight and the xcex1-olefin content (xcex1t) is more than 15% by weight, the obtained composition may tend to be deteriorated in transparency.
The content of the cold xylene solubles (CXS) contained in the propylene-based copolymer composition is preferably in the range of 10 to 60% by weight based on the weight of the whole polymer. When the CXS is less than 10% by weight, the obtained composition may tend to be insufficient in flexibility. On the other hand, when the CXS is more than 60% by weight, the obtained composition may tend to be deteriorated in heat resistance.
Also, it is preferred that the content of the xcex1-olefin other than propylene having 2 to 8 carbon atoms (xcex1t: wt. %) and the content of the cold xylene solubles (CXS: wt. %) satisfy the following formula:
CXS greater than 5xcex1txe2x88x9225 (5xe2x89xa6xcex1txe2x89xa615) 
When the CXS does not satisfy the above formula, the obtained composition may tend to be deteriorated in transparency.
The propylene-based copolymer composition capable of satisfying the above properties exhibits a melting point substantially identical to that of propylene homopolymer, and a melting peak temperature as high as not less than 160xc2x0 C. This indicates that the propylene copolymer has a high heat resistance.
The thus obtained propylene-based copolymer composition can exhibit a flexural modulus of usually 100 to 600 MPa, preferably 150 to 500 MPa when measured at 23xc2x0 C. according to JIS K7203; a tensile strength at break of usually not less than 30 MPa when measured at 23xc2x0 C. according to JIS K7113, and a haze of a 2 mm-thick sheet of usually not more than 70% when measured according to JIS K6717.
The propylene-based copolymer composition of the present invention is obtained by first producing the component (A) by polymerization and then producing the component (B) by polymerization in the presence of the obtained component (A).
For example, the composition is preferably produced by at least two-stage polymerization method. That is, the propylene homopolymer is produced by the first-stage polymerization, and then the copolymer of propylene and the xcex1-olefin other than propylene having 2 to 8 carbon atoms which contains propylene and ethylene as essential components, is produced by the second or subsequent-stage polymerization, thereby obtaining such a composition having a propylene content of 85 to 95% by weight based on the weight of the whole polymer and an xcex1-olefin content (xcex1t) of 5 to 15% by weight based on the weight of the whole polymer.
The catalysts usable in the above successive polymerization are not particularly restricted. As the suitable catalysts, there may be used those catalysts comprising an organoaluminum compound and a solid component containing titanium atom, magnesium atom, halogen atom and an electron donating compound as essential ingredients.
As the organoaluminum compounds, there may be used those compounds represented by the following formula:
R1mA1X(3-m) 
wherein R1 is a hydrocarbon group having 1 to 12 carbon atoms; X is a halogen atom; and m is a number of 1 to 3.
Examples of the organoaluminum compounds may include trialkyl aluminums such as trimethyl aluminum and triethyl aluminum; dialkyl aluminum halides such as dimethyl aluminum chloride and diethyl aluminum chloride; alkyl aluminum sesquihalides such as methyl aluminum sesquichloride and ethyl aluminum sesquichloride; alkyl aluminum dihalides such as methyl aluminum dichloride and ethyl aluminum dichloride; alkyl aluminum hydrides such as diethyl aluminum hydride; or the like.
As sources of the titanium atom contained in the solid component containing titanium atom, magnesium atom, halogen atom and an electron donating compound as essential ingredients, there may be exemplified those titanium compounds represented by the following formula:
Ti(OR2)(4-n)Xn 
wherein R2 is a hydrocarbon group having 1 to 10 carbon atoms; X is a halogen atom; and n is a number of 0 to 4.
Among these titanium compounds, titanium tetrachloride, tetraethoxy titanium, tetrabutoxy titanium or the like are preferred.
Examples of magnesium compounds used as sources of the magnesium atom, may include dialkyl magnesium, magnesium dihalide, dialkoxy magnesium, alkoxy magnesium halide or the like. Among these magnesium compounds, magnesium dihalide is preferred. As the halogen atoms, there may be used fluorine, chlorine, bromine and iodine. Among these halogen atoms, chlorine is preferred. The halogen atom may be usually supplied from the above titanium compounds or magnesium compounds. However, the halogen atom may be supplied from other halogen sources such as aluminum halides, silicon halides, tungsten halides or the like.
As the electron donating compounds, there may exemplified oxygen-containing compounds such as alcohols, phenols, ketones, aldehydes, carboxylic acids, organic or inorganic acids and derivatives thereof; nitrogen-containing compounds such as ammonia, amines, nitriles and isocyanates; or the like. Among these electron donating compounds, inorganic acid esters, organic acid esters, organic acid halides, etc., are preferred, and silicic acid esters, phthalic acid esters, cellosolve acetate, phthalic halide, etc., are more preferred.
As the silicic acid esters, there may be exemplified organosilicon compounds represented by the following formula:
R3R4(3-p)Si(OR5)p 
wherein R3 is a branched aliphatic hydrocarbon residue having 3 to 20, preferably 4 to 10 carbon atoms, or a cyclic hydrocarbon residue having 5 to 20, preferably 6 to 10 carbon atoms; R4 is a branched or linear aliphatic hydrocarbon residue having 1 to 20, preferably 1 to 10 carbon atoms; R5 is an aliphatic hydrocarbon residue having 1 to 10, preferably 1 to 4 carbon atoms; and p is a number of 1 to 3.
Examples of the preferred organosilicon compounds may include tert-butyl-methyl-dimethoxysilane, tert-butyl-methyl-diethoxysilane, cyclohexyl-methyl-dimethoxysilane, cyclohexyl-methyl diethoxysilane or the like.
The propylene-based copolymer composition of the present invention can be produced by the following two-stage polymerization method. Namely, at the first stage, propylene or propylene and other xcex1-olefin having 2 to 8 carbon atoms are supplied to conduct the polymerization of xcex1-olefin containing propylene as a main component at a temperature of 50 to 150xc2x0 C., preferably 50 to 100xc2x0 C. under a propylene partial pressure of 0.5 to 4.5 MPa, preferably 1.0 to 3.5 MPa in the presence of the above-described catalyst, thereby producing the component (A). Then, at the second stage, propylene and ethylene, or propylene, ethylene and xcex1-olefin having 4 to 8 carbon atoms are supplied to conduct the copolymerization between propylene and ethylene or between propylene, ethylene and the xcex1-olefin at a temperature of 50 to 150xc2x0 C., preferably 50 to 100xc2x0 C. under propylene and ethylene partial pressures each being 0.3 to 4.5 MPa, preferably 0.5 to 3.5 MPa, in the presence of the above-described catalyst, thereby producing the component (B).
The above polymerization reactions may be conducted by either a batch process, a continuous process or a semi-batch process. The first-stage polymerization may be carried out in gas phase or liquid phase, and the second-stage or subsequent polymerization may also be carried out in gas phase or liquid phase, preferably in gas phase. The residence time at each stage is 0.5 to 10 hours, preferably 1 to 5 hours.
In the process of the present invention, the respective contents of the components (A) and (B) may be controlled by amounts of monomers to be polymerized at each stage, and the isotactic index of the component (A) may be controlled by kind of catalyst used, polymerization conditions (such as temperature and pressure) or composition of monomers charged. In addition, the cold xylene insolubles or cold xylene solubles of the component (B) may be controlled by composition of monomers charged at each stage, amounts of polymers produced at each stage and molecular weights thereof (the molecular weights can be adjusted, for example, by amount of hydrogen supplied), as well as by kind of catalyst selected.
Further, it is preferred that the xcex1-olefin content (xcex1t) is controlled by composition of monomers charged at each stage, and the CXS and the melting peak temperature are controlled by the ratio between amount of polymers produced at the first stage to that produced at the second and subsequent stages or molecular weights thereof which can be adjusted, for example, by amount of hydrogen supplied.
In the case where the polymers produced by the above methods cause problems such as sticky polymer particles, it is preferred that an active hydrogen-containing compound is added in an amount of 100 to 1,000 moles based on one mole of titanium atom contained in solid component of the catalyst or in an amount of 2 to 5 moles based on one mole of the organoaluminum compound contained in the catalyst in order to impart a good fluidity to the particles.
Examples of the active hydrogen-containing compounds may include water, alcohols, phenols, aldehydes, carboxylic acids, acid amides, ammonia, amines or the like.
The propylene-based copolymer composition of the present invention may further contain ethylene-based polymers such as ethylene/xcex1-olefin copolymer and ethylene/vinyl acetate copolymer, propylene-based polymers such as propylene/xcex1-olefin copolymer and syndiotactic polypropylene, and hydrogenated products of block copolymers of styrene and conjugated diene such as butadiene and isoprene, unless the addition thereof adversely affects the transparency or heat resistance of the obtained composition. Also, xcex1-crystal nucleating agents ordinarily used for enhancing the transparency of propylene-based polymers may be added to the composition. Further, rubber softening agents may be blended in the composition in order to impart a good flexibility thereto.
Furthermore, the propylene-based copolymer composition of the present invention may contain, if required, various resins or rubbers other than those described above, fillers such as glass fibers, calcium carbonate, silica, talc, mica and clays, various additives such as antioxidants, light stabilizers, anti-static agents, lubricants, dispersants, neutralizers and flame retardants, and the like unless the addition thereof adversely affects the effects of the present invention.
The propylene-based copolymer composition of the present invention can be molded into a desired shape by various molding methods used for polyolefins such as extrusion molding method, injection molding method, compression molding method or the like, in order to produce single products, laminates with other materials or the like.
Thus, the propylene-based copolymer composition of the present invention exhibits not only good heat resistance, flexibility and transparency, but also excellent mechanical properties such as tensile strength at break and impact resistance.